RonBee told me that he guesses that the sentence: she went to the theatre "on the underground" means "by subway".
I have read that the preposition on is just used to indicate the presence of a person inside the vehicle and not the waz zou get somewhere.
Is the my interpretation completely wrong? I thought they meant that the theatre was placed on the underground.
"they went to the theater on the subway"
can be paraphrased
'they went on the subway'
which means that, yes, they were inside the vehicle
no contradiction there